1. Field of the Invention
This invention relates to a new and improved street sweeper and more particularly to a new and improved power management system for operating the various components of a street sweeper including such components as the vacuum fan, side brooms, the conveyor, and the like.
2. Description of the Prior Art
Single-engine street sweepers, such as disclosed in U.S. Pat. Nos. 4,343,060, and 4,328,603, each incorporated by reference herein, use the vehicle chassis engine to power the vehicle as well as the sweeping apparatus. Known sweepers typically use one or more hydraulic pumps driven by one or more power transmissions, such as a power-take-off (PTO) attached to the vehicle transmission.
Street sweepers operate at a variety of sweeping speeds, often up to 15 mph or more, and are required to negotiate slowly around obstacles, such as parked cars, while sweeping. Engine speed varies substantially as the travel speed varies during operation, such as from 1 to 15 mph. For example, at an idle the engine speed may be approximately 700 rpm, while at maximum travel speed (maximum throttle) the engine speed may be approximately 2000 RPM. The horsepower produced by the vehicle engine changes significantly within this range of engine speeds. For any given mechanical apparatus, functionality at low engine speeds may be limited as the horsepower may be insufficient to drive the associated pumps, actuators, etc.
Typically, street sweepers have onboard water spray systems to reduce dust clouding. These onboard spray systems are inefficient for having limited water capacity and requiring frequent refilling. Street sweepers typically do not have active dust suppression systems. During certain operations street sweepers may generate an objectionable airborne dust cloud. In residential areas the creation of a dust cloud may be especially objectionable. To minimize dusting, water may be applied to the surface prior to sweeping, such as via a water truck progressing ahead of the street sweeper. The additional step of applying water to the surface is economically and ecologically inefficient and undesirable. As a result, the sweeping operation may be limited during particularly dry or dusty periods. Assignee's U.S. patent applications Ser. No. 10/235,965, entitled “Retractable Broom and Dust Skirt”, filed Sep. 4, 2002; Ser. No. 10/236,095, entitled “Street Sweeper”, filed Sep. 6, 2002; Ser. No. 10/236,094, entitled “Street Sweeper”, filed Sep. 6, 2002, each application being incorporated by reference herein, disclose aspects of a street sweeper having an active dust suppression system.
Certain air sweepers, such as disclosed in U.S. Pat. Nos. 4,109,341; 4,807,327; 5,794,304; and 5,852,847 have air pressure systems for moving a sufficient amount of air across the ground surface to capture debris for subsequent collection. The air pressure systems typically include a relatively large driven fan. It is recognized that significant fan horsepower is required to sweep large amounts of debris and control airborne dust. In some instances, a dedicated engine (separate from the vehicle engine) is used to power air pressure systems of an air sweeper.
Fixed displacement or variable displacement hydraulic pumps driving fixed displacement hydraulic motors to rotate main brooms, side brooms, and conveyors, have been commonly used on street sweepers for a number of years. Hydraulic flow from a single pump is directed to two or more hydraulic motors for driving rotating sweeping components.
Variable displacement hydraulic pumps which are hydraulically pressure-flow compensated to provide a single constant output in gallonage within a given range of input speeds also have been known for a number of years.
Manually controlled variable displacement hydraulic pumps have been used to obtain a desired output in gallons per minute even though the input speed is constantly changing.
U.S. Pat. No. 4,343,060, incorporated by reference herein, discloses the use of a hydraulic system for a street sweeper which incorporates a variable volume hydraulic pump which is electronically controlled to provide a choice of three or more constant output speeds of the rotating sweeping components as the vehicle engine speed changes from between 1000–3000 RPM to provide optimum broom and conveyer speeds regardless of engine speed.